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Will an AR-15 Jig Work on an AR-9? Size Compatibility

Jigs can be used to create functional rifles with parts the ATF doesn’t consider to be firearms. Of course, these 80% lowers need additional work to become capable of firing, but with a jig, you can make these weapons work just like one from a factory. So will an AR-15 jig work on an AR-9?

The AR-15 jig will work with an AR-9. These jigs are made to make improvements to create working firearms. The calibers should not come into question as they are only used to drill holes for the safety mechanism and don’t impact the barrel’s caliber.

Working with 80% lowers to develop them into regular operational firearms will take someone with the know-how and the tools to make it work. Don’t sweat it! Once you’ve drilled out a few lower receivers, the process becomes more manageable. So read on and learn all you need to know about using your AR-15 jig on your AR-9.

How Jigs Work on the AR Rifle Platform

Jigs are made to work with what is called and 80% lower. 80% lower are the lower part of an AR-15 rifle that can’t fire. The internal workings, like the trigger mechanism, have been removed, and none of the proper holes have not been drilled for the safety or selector switches.

By not drilling the holes and installing the other parts, arms dealers can sell these 80% lowers without the ATF’s knowledge, and you can assemble the rifle at home at your leisure. However, be aware that this process creates a gun that is against the law in some states as it will not have a serial number or have to go through a background check.

The way that a jig works on the body of your AR are:

  • Template – Jigs work like a template to tell you where to drill and mill out the metal pieces in the proper places. The jig will line up when laid out atop the rifle and can be used as often as possible.
  • Depth – The jig also prevents the drilling from burrowing too deep in the metal. Depth is essential when working with 80% lowers because if you make a mistake, the blank is ruined, and you must start over. Too much depth on a drill or mill could make the rifle not function.

Once the holes are drilled and the pieces of metal are cleared away, you can work on installing the trigger and safety mechanism. Again, the jig serves the purpose of showing the gunsmith where to install the holes on the surface of your 80% lower.

I use either Brownells, Palmetto State Armory, or Optics Planet to buy parts, that way I always know what I’m getting and that it will actually show up.

Does AR-9 Use the AR-15 Lower Parts Kit?

The AR-9 uses the same lower parts kit as an AR-15. This is because the jig only works with the lower portion of the rifle, not the barrel or bolt assembly group. Therefore, when dealing with things like the trigger and magazine well, you only need to make a few holes and install the necessary pieces.

Some of the pieces in an AR-15 lower parts kit are:

  • Trigger Spring – The spring that gives tension to the trigger is tiny and could be hard to source. Buying it in a lower parts kit means you will get the correct part and won’t have the hassle of returning it.
  • Bolt Catch – The bolt catch is another piece you will find in the parts kit. It holds the bolt back so you can inspect the chamber and top of the magazine well. It is vital to the rifle’s life, and you should check it for flaws before installation.
  • Selector Spring – The selector switch spring is what keeps the tension on the switch when you move from firing modes. This tension is essential because you wouldn’t be able to control the rifle without it, and it would fire like an automatic or single shot.

What is the Difference Between AR-15 and AR-9?

The most significant difference between the two is the round. With an AR-15, you can fire two types of ammo. With an AR-9, you get the same rifle style but only a 9mm round. Often you can even use handgun mags instead of the traditional PMag style. Users rave about the interchangeability and availability of decent ammunition.

The significant differences between the AR-15 and AR-9 are:

  • Compatibility – The AR-15 is a platform that has been styled in so many ways that lower receivers for calibers like the .308 are becoming more common. The compatibility between AR-15 style rifles and the AR-9 does not work because the 15 styles can come in so many different calibers and the 9 in only a single one.
  • Spring Driven – The 9mm round is powerful on impact but doesn’t require the oomph that a 5.56 NATO round does. The AR-15 rifle must have a spring in the butt to allow it to return to the firing position. AR-9 only needs a buttstock on the gun, not any extra springs to handle the recoil.
  • Magazines – Another big difference between the rifles is their magazine size use. Both platforms are the same size, with the mag well on the 15 style often relatively larger to accommodate the larger rounds.

The AR platform isn’t one of the most copied styles on the planet for no reason. The weapons are easily modified and upgraded and can have smaller versions like the AR-9, which is more of a handgun style than a rifle.


The jig on the 80% lower of an AR-15 will also work on the body of the AR-9 rifle. The nine fires a 9mm round that is similar to what is fired from a handgun. The rifles can be drilled with the jigs as templates to create weapons from blank lowers.

The size differences between the rifles are sometimes the most significant. When you want to fire a larger round, you can be assured that the AR-15 style platform will handle it.

The AR-9 is an excellent home defense rifle that can protect you and your family against intruders without shooting up the houses around you if trouble jumps off.